A rural principal arterial is expected to carry an ESAL of 0.188 x 106 during the first year of operation with an expected annual growth of 6% over the 20-year design life. If the subgrade has a resilient modulus of 15,000 lb/in2, design a suitable pavement consisting of a granular subbase with a layer coefficient of 0.13, a granular base layer with a layer coefficient of 0.14, and an asphalt concrete surface with an elastic modulus of 400,000 lb/in2. Assume all mi values = 1, the percent of traffic on the design lane is 47%, and SN = 4. Use a reliability level of 85%, a standard deviation of 0.45, and a design serviceability loss of 2.0.

Question

What will be an ideal response?

Answer 1

First, determine design ESAL
The design lane use factor, fd, is 0.47
From Table 19.4, Gjt = 36.79
Total ESALi = (0.47)(36.79)(0.188 × 106)
ESAL = 3.25 × 106
Using the nomograph in Figure 19.10,
Step 1: Connect Reliability of 85% to standard deviation of 0.45 and
extend to first turning line to create “A”
Step 2: Connect “A” to ESAL of 3.25 × 106 and extend to second turning
line to create “B”
Step 3: Connect “B” to Mr of 15 × 103 and extend to design serviceability
loss chart to create “C”
Step 4: Connect “C” to ?PSI of 2.0
Step 5: Draw vertical line to read SN of 3.1
Determine structural coefficients for each layer
From Figure 19.5, with EAC = 400,000 lb/in2
a1= 0.40
Since this pavement is being designed with three layers, equation 19.6 can be
modified for use in this problem as:
SN = a1D1 + a2D2m2 + a3D3m3
3.1 = (0.40)D1 + (0.14)D2(1) + (0.13)D3(1)
From Table 19.11, for 3.25 × 106 ESALs, a recommended minimum
thickness of asphalt concrete is 3.5 inches and 6 inches for aggregate base.
The depth of subbase can then be found:
3.1 = (0.40)(3.5) + (0.14)(6)(1) + (0.13)D3(1)
D3 = 6.6 inches ? round up to 7 inches.